The effects of Hange-shashin-to (TJ-14) on cholera toxin-induced intestinal fluid secretion were studied to elucidate the mechanism by which this kampo medicine manifests antidiarrheal effects. TJ-14 suppressed the intestinal fluid secretion induced by cholera toxin (1 μg/rat) in a dose-dependent manner at doses between 125 and 1000 mg/kg. It also inhibited the luminal prostaglandin E₂ (PGE₂) level. On the other hand, serotonin (5-HT) release was not affected by TJ-14. Subcutaneous injection of indomethacin at 10 mg/kg or ondansetron at 100 μg/kg significantly suppressed intestinal secretion. The luminal PGE₂ level was also inhibited by indomethacin (10 mg/kg, s.c.). TJ-14, even at 10^-4 g/ml, and little effect on the phasic contration of isolated guinea pig ileum induced by 5-HT (2×10^-6 g/ml), while ondansetron suppressed the phasic contraction caused by 5-HT.These results indicate that TJ-14 is useful in suppressing cholera toxin-stimulated intestinal fluid secretion, and that this effect is partially due to its suppressive action on the PGE₂ level.